Multi-purpose power hand tools provide a variety of capabilities for the user, including sawing, drilling, and driving threaded fasteners among others. One class of prior art multi-purpose power hand tool includes a universal drive or power module for supplying shaft power to special-purpose accessories such as rotary cutters which are mounted to the power module. The reconfiguration achieved by mounting different accessories to the output shaft of the power module in this way provides all the advantages of a special-purpose tool without the associated cost, as the tools are able to share a common power supply, controls and motor.
Cordless power tool systems including releasably attachable common battery units selectively attachable to each of a range of tools are well known in the art. Each tool incorporates its own motor and accessories such as rotary blades or chucks. Incorporating a common battery unit makes the complete system more economical since battery packs are relatively high cost components. Various simple sliding couplings are used for electrically and mechanically coupling a battery pack with the tool housing, allowing the batteries to be readily installed and removed.
U.S. Pat. No. 6,181,032 describes a modular, cordless electric tool system with a power handle module to which different special-purpose tools may be fitted. The motors, or the like, of the special-purpose tools are controlled by a trigger on the power handle module. A finger-releasable latch is provided on the power handle module for mechanically fastening it to the special-purpose tool. This latch is interlocked with the trigger to avoid powering the special-purpose tool when connecting it to the power handle module. An actuator connected to the trigger extends through the interface between the two components to engage a switch in the special-purpose tool.
One of the drawbacks associated with all the above-mentioned multi-purpose power hand tools and cordless power tool systems is associated with the controls or switches required for operating them. None of these prior art devices teaches a modular hand tool system able to provide the desired safety and functional features which would allow a universal power handle module to power and control a saw and a reversible power tool. For instance, on power saws, in order to prevent accidental actuation of the motor, a safety switch is typically releasably interlocked with the trigger switch, so that both the safety and trigger switches must be simultaneously actuated to operate the saw blade. In many prior art saws, the safety switch is a button-type switch mounted on a side of the handle. In order to operate the saw, the handle must be gripped, and the user then simultaneously depresses the button-like safety switch with the thumb while squeezing the trigger with one or more of the other fingers of the same hand.
A functional necessity for multi-purpose tools is the ability to provide a control appropriate to the specific operational characteristics required for the tool. Providing a reversible power tool for driving threaded fasteners requires a direction switch to allow the user to select the direction of rotation before squeezing the trigger to rotate the chuck. For special-purpose tools such as fastener drivers, modulating-type control for allowing control of the motor speed is desirable while for circular saws or lamps it would be preferable to have on-off type control.
It is an object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages or more generally to provide an improved multi-purpose power hand tool.